1. Field of the Invention
The invention relates to a reproducing or recording device for reproducing, or recording on, an optical recording medium. Furthermore, the invention relates to a corresponding device having a circuit arrangement for a phase-locked loop, also termed a tracking synchronization circuit, having a phase detector for comparing a reference signal with a tracking signal, and for supplying an output value corresponding to the phase shift between the reference and tracking signals, and having a controller, which is connected to the output of the phase detector and leads to the input of a tracking oscillator.
2. Description of the Prior Art
So-called phase-locked loop or PLL circuits for tracking synchronization are known in control engineering. The aim of such circuits is to set the frequency of an oscillator such that it corresponds to the frequency and phase of a reference oscillator. The frequency of the tracking oscillator can be varied with the aid of a control voltage. So-called voltage-controlled oscillators (VCO) are used as oscillators. Analog computer oscillators or function generators can be used for low frequencies. Suitable for use at higher frequencies are emitter-coupled multivibrators or else any LC oscillator by connecting a variable capacitance diode in parallel with the resonant circuit. The phase detector used supplies an output voltage which is determined by the phase shift between the tracking AC voltage and the reference AC voltage.
It is true that digital phase detectors are used in the case of known devices with digital phase-locked loops, but recourse is made to analog VCOs for the tracking oscillator. Such circuit arrangements suffice for applications with a defined hold range. However, there are problems when signals of different frequency reach the phase-locked loop. In such cases, the data rate or the frequency of the input signals can lie outside the hold range, as a result of which the phase-locked loop ceases to be locked and reliable operation is no longer ensured. In such cases, the centre frequency of the analog VCO must be reset, and this leads to increased outlay on circuitry.
Known devices with a digital phase-locked loop can therefore certainly be expanded with regard to the frequency range which can be processed, by being switching over but the control precision is reduced since the aim will be to prescribe the hold range to be as wide as possible in order to minimize the outlay for switching over.
It is therefore the object of the invention to specify a reproducing or recording device for reproducing, or recording on, an optical recording medium having a circuit arrangement for a phase-locked loop, which has a high control precision and is capable of processing a wide input frequency range without the need for the discrete resetting of the centre frequency as a function of the input frequency.
This object of the invention is achieved by means of a device in accordance with the features of the independent patent claims, advantageous and expedient embodiments and developments of the invention being specified in the subclaims.